Distribution and origin of rare earth elements (REEs) in topsoils and soil profiles of southern Konya (Turkey): Implication for controls on the dynamics of REEs in soils and bedrocks

Abstract

The distribution of rare earth elements (REEs) was investigated in topsoils, soil profiles, bedrocks, and stream sediments collected from different geological environments in southern Konya to understand how natural and anthropogenic factors affect the geochemical behavior of REEs and the dynamics of pedogenic processes. The highest REE concentrations were observed in volcanic rocks and the lowest REE concentrations were observed in sedimentary rocks. The soils derived from volcanic rocks show the highest average REE content, followed by soils derived from sedimentary rocks and then soils derived from ophiolitic rocks. REE contents in soils derived from different geological units decrease in the following order: volcanic > sedimentary > ophiolitic. The average REE concentrations of soils in the study area are in decreasing order: Ce > La > Nd > Pr > Sm > Gd > Dy > Er > Yb > Eu > Tb > Ho > Tm > Lu. (La/Yb)N ranged from 1.19 to 1.86 with an average value of 1.5 indicating considerable enrichment of LREEs in topsoil. The highest LREE/HREE fractionation was determined in the soils over sedimentary rocks. The soils have slightly negative Ce anomaly (Ce/Ce*= 0.98 to 0.99) and positive Eu anomaly (Eu/Eu* = 1.02 to 1.12). REEs in the soil profile developed on sedimentary rocks (Profile-I; HPPR) were higher than those developed on ophiolitic rocks (Profile-II; KHPR). The soil profile samples show slightly negative Ce anomalies (Profile I=0.93, Profile II=0.93) and positive Eu anomalies (Profile I=1.08, Profile II=1.39) similar to topsoils. The spatial distribution of REEs normalized to the Upper crust and Earth crust showed that parental materials control the prevalence of REEs in soils of southern Konya. The distribution of REEs with Eu and Ce anomalies in the soils is similar to REEs with Eu and Ce anomalies in the parental rocks. The spatial distribution of REEs in soils appears to be controlled by the lithology of the study area as well as mineral composition, weathering process, and pH. Enrichment factors (EF) and geoaccumulation index (Igeo) commonly indicating non-enriched soils correspond to natural materials.